GOME-2 description

The Global Ozone Monitoring Experiment-2 (GOME-2) is a scanning spectrometer that captures light reflected from the Earth's surface and atmosphere. The spectrometer splits the light into its spectral components to map concentrations of atmospheric ozone as well as nitrogen dioxide, sulphur dioxide, other trace gases and ultraviolet radiation.

The GOME-2 instrument is mounted to the flight direction side of the MetOp satellite. The entire instrument is housed in a box measuring just 85 x 65 cm. Most of the instrument is covered with a protective thermal foil.

The GOME-2 instrument consists of the following units:

Spectrometers

GOME-2 contains two spectrometers – one each for polarised and unpolarised light.

The main spectrometer (for unpolarised signal) splits incoming light into four channels. It does this by a complex array of telescopes and prisms. Detectors at the end of each optical path collect information about the signal in each channel.

Prisms inside the main spectrometer also separate the polarised components (s- and p- channels) and direct these into a second spectrometer that detects polarised radiation. Information about the light in each channel is passed into the Polarisation Unit (PU) electronics.

Block diagram of GOME-2 optics, with the differences to GOME-1 highlighted

Polarisation Unit (PU)

The Polarisation Unit comprises the spectrometer and detection electronics. The polarisation data is needed for a radiometric correction of the nadir measurement, but contains much more information. It can be used for cloud or aerosol detection, or for high spatially, low spectrally resolved atmospheric-radiance measurements. GOME-2 is unique in being able to do this.

The Calibration Unit optics (new WLS part highlighted in yellow)

Calibration Unit (CU)

The Calibration Unit contains calibration sources providing broad band and spectral line signals. In addition, it contains a diffuser allowing solar calibration to be performed. Together these meet the need for exact radiometric accuracy.

Focal-Plane Assemblies (FPAs)

Each spectrometer channel (six in total) feeds onto a separate 1024 element silicon photodiode array. The main spectrometer FPAs are cooled to –38º C to obtain maximum sensitivity whilst the polarised channels' FPAs are run at 0º C. These feed the FPA electronics, made up of two boards. One board is mounted close to the detector (low noise amplification) and the second mounted on top of the spectrometer objective (filtering, 16-bit A/D conversion and interfaces).

Scan Unit (SU)

The Scan Unit (SU) contains a rotating mirror, situated optically in front of the spectrometer, and its related mechanics and electronics. It scans in the across-track direction to perform global Earth coverage in 1.5 days. All scans can be in-flight reprogrammed, allowing an almost unlimited choice of profiles.

GOME-2 block diagram and electrical interfaces

Control and Data Handling System (CDHS)

The Control and Data Handling System consist of the Control and Data Handling Unit (CDHU) and the GOME Power Distribution Unit (GPDU). All electrical and operational interfaces to GOME-2 are routed through the Control and Data Handling Unit (CDHU). Within this unit, a primary processor is responsible for all Instrument Control Unit (ICU) functions.